The invention relates to a device for capturing wind energy in order to produce electrical energy.
Devices for capturing the energy supplied by the wind, or wind turbines, comprising a vertical mast, a nacelle mounted so that it can rotate about a vertical axis on the upper part of the mast, and at least one capture unit carried by the nacelle, are known. The unit for capturing the wind energy comprises at least one turbine rotor consisting of a hub mounted so that it can rotate on the nacelle about an approximately horizontal axis and at least two blades (generally two or three blades) fixed to the hub in approximately radial directions.
The nacelle, which is generally streamlined, is oriented, automatically or by command, in such a way that the horizontal axis of rotation of the hub is directed into the wind and so that the turbine rotor is rotated at a certain speed which depends on the wind speed.
The energy recovered by the turbine rotor of the wind turbine can be used in different ways and, in particular, this energy can be converted into electrical energy which can be used locally at the site of the wind turbine or sent to a distribution grid.
In this case, the capture unit of the wind turbine also constitutes a unit for producing electrical energy and comprises an electric generator having at least one rotor secured to the turbine rotor and at least one stator fixed to the nacelle.
A first problem encountered in the case of units for capturing wind energy and producing electrical energy relates to the need to make the rotor the electric generator rotate at a sufficiently high speed, by rotation of the turbine rotor. To achieve that, it is generally necessary to use mechanical step-up gearing between the turbine rotor and the generator rotor. Such a device makes the wind turbine more complicated to construct and to maintain.
It has also been proposed for at least two turbine rotors mounted on one and the same axis and rotating in opposite directions to one another to be combined for driving the electric generator. In this case, it is necessary to provide means of mechanical connection between the two turbine rotors so as to drive and to regulate the rotational speed of the rotor of the electric generator.
Such mechanical connection devices are complex and considerably increase the size of the functional part of the wind turbine.
When two contra-rotating turbine rotors are used, a first turbine rotor is directed into the wind and the second turbine rotor, which follows on from the first turbine rotor in the direction of the wind, uses at least some of the recoverable energy of the wind which was not captured by the first turbine rotor.
The devices for mechanical connection between the turbine rotors do not generally allow the two turbine rotors to operate ideally, whatever the wind speed, that is to say do not allow operation such that the combined energy produced over a given period, for example over a year, is as close as possible to the maximum combined recoverable amount of energy.
In other words, there is not yet known any means that allows the operation of the first and of the second contra-rotating turbine rotors to be optimized according to the wind speed.
When the wind speed increases, above and beyond the wind turbine start-up speed, at a certain wind speed aerodynamic stall occurs or is brought about, providing some regulation of the operation of the wind turbine. It is necessary to provide mechanical means, for example devices for adjusting the pitch of the blades of the turbine rotors of the wind turbines, in order to stall or feather the turbine rotors, that is to say bring the blades into a position not subjected to the wind, under desired conditions. These mechanical devices are complex and may increase the risks of breakage and wear of the wind turbine in service.
Furthermore, the driving of the rotor or of the electric generators, off one or more turbine rotors, entails the use of mechanical means which increase the size of the capture units, particularly in the direction of the axis of rotation of the turbine rotors and of the generator rotors.
It is therefore preferable to provide a direct connection between the turbine rotor and the generator rotor. This type of drive cannot be used in the case of electric generators of current type. The use of make it possible to make an easier connection with the turbine rotor of the wind turbine and to increase the compactness of the capture unit of the wind turbine in the axial direction. However, such generators of the discoid type have never been used in wind turbines with contra-rotating turbine rotors.
The object of the invention is therefore to provide a device for capturing wind energy to produce electrical energy, comprising a vertical mast, a nacelle mounted so that it can rotate about a vertical axis on the upper part of the mast and at least one capture unit comprising at least one turbine rotor consisting of a hub mounted so that it can rotate on the nacelle about an approximately horizontal axis and at least two blades fixed to the hub in approximately radial directions and an electric generator having at least one rotor connected to the turbine rotor such that it is driven in rotation by the turbine rotor and at least one stator fixed to the nacelle, it being possible for this device to be obtained compactly while at the same time exhibiting high installed power and making it possible to increase the amount of energy produced during a reference period, for example over the course of one year.
To this end, the capture device according to the invention comprises a first capture unit and a second capture unit, these respectively comprising a first and a second turbine rotor which contra-rotate and are arranged one on each side of the vertical axis of the mast, the hubs of which are mounted to rotate independently of one another about aligned axes and a first and a second electric generator produced in discoid shape and each comprising:
at least one rotor having at least one disc-shaped part secured to the corresponding turbine rotor,
at least one stator having at least one disc-shaped part facing the rotor, and
power electronics means associated with the generator to allow the speed of the rotor to be regulated independently on each of the capture units.
The invention also relates to a method for regulating the capture device in order to optimize its operation so as to produce the maximum combined energy over a reference period.
In order to make the invention easy to understand, a device for capturing wind energy and for producing electrical energy according to the invention and its optimized use for producing a maximum combined amount of energy over a reference period will now be described by way of example with reference to the appended figures.